In today's subscriber access networks—also referred to simply as access networks, increasingly wide use is being made of the subscriber access, embodied for example in accordance with an xDSL transmission method and providing high transmission rates. The broadband Internet access which such a device typically allows will mean a continuing increase in applications provided by these subscriber access networks. One of these applications is the transmission of information with multimedia content—also referred to as broadband multimedia data streams—such as videos or video streams for example. Broadband distribution services, especially multimedia distribution services (e.g. radio and television) as well as on-demand services such as “video-on-demand” or broadband Internet communication (e.g. video conferencing) can be implemented with the aid of these applications for example.
Broadcasting services such as multicasting will increasingly be employed for the transfer of broadband multimedia data streams via communication networks. Multicast—also referred to as IP multicast in communication networks embodied according to the Internet Protocol IP—enables a plurality of recipients to be supplied simultaneously with multimedia data, over the Internet or over another communication network, if necessary in real time as well, without imposing too great a load on servers, routers or the network. Within the framework of multicast there can be any number of recipients which also do not have to be known to the sender. All recipients belonging to a group of interested parties are grouped together under a group address. The sender sends the data only once to this address. For the recipients the data is only multiplexed by those routers at which there are branches in the network structure. This keeps the volume of data to be transmitted smaller since no unnecessary packets will be sent. In addition the load will be relieved on the network and the performance of servers and routers improved. IP multicast is cost effective, especially with transmission services such as multimedia streaming.
The membership of the group is administered in IP networks within the framework of the Internet Group Management Protocol or IGMP. With the Internet Group Management Protocol IP hosts divide up their multicast membership between adjacent multicast routers. In this context a router can also appear as a host, with the group membership of the connected hosts then being combined and reported by the router to a higher-ranking network as a single group membership. IGMP is viewed as a component of the Internet Protocol since a normal IP packet is generated here too containing IGMP information (protocol elements) in its information field.
The Ethernet transmission method is widespread in the subscriber access network, with access being subject to certain general conditions in such networks. For example the user must be able to sign on and be authenticated in an operating system-independent manner; in addition billing information generally has to be recorded. This service feature has been realized for dial-in nodes with the Point-To-Point Protocol (PPP) and the associated radius protocol. The clear solution was thus to expand the procedures and protocols introduced in this area to broadband access, which eventually led to the introduction of “PPP over Ethernet (PPPoE)”.
In current subscriber access networks a plurality of users (hosts) are connected for example via xDSL modems to a decentralized communication device or multiplexer device (also referred to as a Digital Subscriber Line Access Multiplexer, DSLAM). In other variants the communication device is implemented for example by an active or passive optical distribution network (AON or PON). The information transferred from the subscribers to the DSLAM is transmitted over a connected communication network—also as referred to as an aggregation network—to a broadband Network Access Server (NAS) or Broadband Remote Access Server (BRAS), the first node, operating at the IP level and usually dealing together with a management network server (radius server) with the tasks of authentication, billing etc. Current subscriber access networks embodied in accordance with xDSL transmission technology operate with ATM (Asynchronous Transfer Mode) as their layer-2 protocol. In the future however, direct Ethernet transmission technology will increasingly be used here as the layer-2 technology. The Network Access Server is mostly also linked into the ATM or Ethernet communication network. An adaptation layer or PPPoE protocol layer arranged in the NAS makes sure that PPP can be transmitted over Ethernet.
PPPoE along with PPPoA is practically a de-facto standard for broadband Internet access. The request for setting up a connection to the Internet—i.e. initialization of a PPPoE-session—is made by the user (PPPoE), with the request being processed by a Broadband Remote Access Server (BRAS) in its role as PPPoE server. One PPPoE session per user is required, with an individual BRAS being able to process up to 50,000 sessions or communication relationships. PPPoE is however only suitable for point-to-point relationships. This was sufficient in most applications, since current accesses to the Internet are mostly based on Unicast data traffic. For innovative services such as Internet TV or Broadcast over DSL this point-to-point topology proves to be a disadvantage. This will be illustrated by an example: In a subscriber access network, 100 TV channels are offered to the subscribers for selection, with a bandwidth of 2 Megabits per second being required for each TV channel. An individual BRAS can process around 50,000 subscribers, i.e. at maximum load 50,000 PPPoE connections or sessions must be processed simultaneously. If each subscriber requests a specific TV channel the BRAS must insert 50,000 TV channels into 50,000 PPPoE connections. This requires a bandwidth of around 100 Gigabits per second. Since PPPoE is based on a point-to-point connection, a BRAS cannot profit from the fact that only 100 different TV channels, i.e. 100 different types of information have to be processed. In the worst case, in which all subscribers request one and the same TV channel, this means that this one requested TV channel still has to be inserted 50,000 times by the BRAS into the 50,000 PPPoE sessions. The result is not only an enormous waste of bandwidth by the BRAS, but also a waste of bandwidth in respect of the network resources available in the aggregation network between BRAS and the respective DSLAM.
To overcome the above problems, as a first measure the capacity of the BRAS and also of the subscriber access network can be embodied such that the complex multicast distribution can be controlled via the BRAS. This solution however involves a high level of technical and thereby also of financial outlay.
A second solution would be the relocation of the multicast distribution point from the respective video source (e.g. video server or head end) to the respective DSLAM. A consequence of this would be that in the DSLAM, as well as the existing PPPoE session between subscriber and BRAS, a further connection for transmission of the multicast data traffic has to be configured over the individual subscriber line. The problem which arises here however is that most of the communication devices arranged on the subscriber side (personal computer, router, set top box) cannot process a plurality of parallel connections or sessions. Thus for example two sessions conducted simultaneously require two different IP addresses—but neither the current subscriber side communication devices or CPEs (Customer Promises Equipment) nor the DSL routers are embodied to operate with a plurality of equal-ranking IP addresses.
There would be the theoretical option of terminating the PPPoE session in the subscriber-side communication device (for example a NAT, Network Address Translation) router as well as terminating the multicast session in a TV set top box connected to the NAT router. This however would make it necessary for the NAT router to “tunnel through” the multicast session to the TV set top box, which involves greater outlay. The 2-session approach thus has the following disadvantages:                The subscriber-side communication device must be equipped with “tunnel attributes”,        Separate cabling is required between the subscriber-side communication device and the set top box for example,        The connection of further set top boxes is very complicated,        The set top box cannot be used as an Internet access for Internet-compliant applications such as the EPG (Electronic Program Guide) or Internet telephony (VoIP) for example,        A personal computer or laptop cannot be employed for utilization of TV channels,        At least two public IP addresses are required for each household.        
An ADSL access network with improved authentication, authorization, billing control and configuration control for multicast services is described in European application EP 1 398 910 A1.
An XDSL device, multicast distribution system and data distribution method are described in American application US 2003/0053458 A1.